Field
Aspects relate to hydraulic valves for shock absorbers (dampers) that control fluid flow.
Discussion of Related Art
Simple passive dampers utilize restrictive valves that produce an exponential pressure drop as velocity increases. Modern passive dampers use multi-stage disc stacks to progressively open orifices as pressure increases. This has the effect of linearizing and even decreasing the slope of force response in the damper as velocity increases.
More complex semi-active dampers utilize fluid restriction mechanisms such as solenoid valves or a magnetorheological fluid to change the force response of the damper based on external inputs. In solenoid-based systems, durability is usually maintained by utilizing multi-stage blowoff valves in the piston head and base valves, which are commonly known in the art. These are generally pressure-activated valves that allow fluid flow to bypass the solenoid based on a fluid pressure.
Recent advances have led to the development of fully active suspensions that can push and pull the wheels of a vehicle in addition to providing damping. Such systems generally provide a substantial improvement in the ride and handling of cars and trucks. One approach to active suspension is with an electrohydraulic actuator that utilizes a damper body with a piston and piston head that separates a compression chamber and a rebound chamber. A hydraulic pump coupled to an electric motor is operatively coupled to the compression and rebound chambers. In such a system, a high damper velocity due to a wheel event such as a pothole hit may lead to extremely high rotational velocity of the hydraulic pump. In some cases this may be undesirable for durability and ride quality reasons. In the prior art, pressure-dependent blowoff valves have been used to limit RPM. These valves are relatively simple to construct and tune; however, they are only moderately effective in an active suspension because they are pressure activated and not fluid velocity (or volumetric flow rate) activated. During situations where the active suspension is controlled to be stiff, the velocity may be low but the pressure high, causing the blowoff to engage prematurely. Alternatively, where the active suspension is controlled soft, the velocity may be high but the pressure low, causing the blowoff to not engage while the pump is at high RPM.